It is a well-known fact that the presence of lipid has various adverse effects on the beer quality and the efficiency of beer brewing process. For example, unsaturated fatty acids inhibit the synthesis of ester components, which are yeast-synthesized flavor components, and oxides of linolenic acid, etc. give beer a stale flavor and damage the flavor stability. In addition, lipid is an anti-foaming agent, and decreases the foam forming, foam lacing and foam stability of beer.
Most of such lipids are derived from malt, the major raw material of beer, and they occur in malt and in the beer brewing process in various forms including simple lipids (fatty acids, triglycerides and other neutral lipids), complex lipids (glycolipids and phospholipids) and bound lipids such as those bound with starch grains. However, not all lipids have an adverse effect, i.e., the balance of these forms of lipids subtly affects the beer quality and the efficiency of beer brewing process; it remains unknown what the balance is appropriate. It is also unknown what the degree of total lipid content is preferable if lipids are to be removed.
With the aim of removing these lipids from the raw material to avoid their adverse effects on the preparation of alcoholic beverages, various methods have been attempted, including (1) removal of germs which contain a higher content of lipids from the raw material cereals (polishing), (2) removal of lipids from the raw material cereals by ethanol extraction, (3) pretreatment of the raw material cereals with lipid decomposing enzyme (Japanese Patent Examined Publication No. 22478/1973, Japanese Patent Unexamined Publication No. 55069/1987) or addition of lipid decomposing enzyme during the preparation process (Japanese Patent Examined Publication No. 21594/1984) and (4) removal of lipids by special filtration-separation.
However, all these methods have various problems. For example, polishing is disadvantageous in that increasing the polishing ratio results in an extremely high cost of raw material, and sufficient lipid removal cannot be achieved even when the degree of polishing is increased, because the center of the embryo of the raw material cereals is rich in lipids.
In the case of removal of lipids by ethanol extraction, there is a problem that enzymes in the raw material cereals are greatly damaged so that an additional process such as enzyme replenishment should be necessary because the raw material cereals are kept in contact with a high concentration of ethanol for a long time and high temperature heating is necessary to remove this ethanol.
In the method using a lipid decomposing enzyme, the bad influence of the substances produced upon enzymatic decomposition appears in alcoholic beverages unless the decomposition substances are removed. There has been no method for removing these decomposition substances which is suitable to the preparation of various alcoholic beverages; the existing removal method is troublesome, and requires a very large number of processes. For example, when using lipase, the amount of free fatty acids increases. A high content of these free fatty acids worsens the filterability and inhibits the synthesis of esters which are flavor components of alcoholic beverages. For this reason, a process is necessary to remove the free fatty acids.
Methods for lipid removal by filtration-separation include a method using a lauter tun, in which a spent grain and insoluble substances are used as a filter layer, a method using a mash filter made of fabric or cotton, and centrifugal separation using a centrifuge. Lipid removal ratio increases in this order, though the time required for filtration-separation also increases.
In filtration-separation using a lauter tun, which is the most effective method in lipid removal ratio among these methods, a fair amount of initial filtrate must be returned to the original to form a stiff filtering layer, through which filtration is conducted. It requires a 1.5 to 2 times longer time than filtration-separation using a mash filter and other methods, and in addition, it is very difficult to control the formation of the filtering layer. In filtration-separation using a mash filter, the lipid removal ratio is very low in the initial portion of filtrate. In the case of centrifugation, the lipid removal ratio is very low due to only solid-liquid separation without the filtering layer. In any method, problems are inevitable, i.e., lipids cannot be sufficiently removed, the removal efficiency is extremely poor, much time is consumed, the costs are high, and the control over filtration-separation is impossible.
Of these methods, the filtration-separation method has been only used for beer brewing, but this method cannot be said to be effective for the reasons described above.
On the other hand, various methods based on extraction with subcritical or supercritical carbon dioxide have recently been attempted for removal of lipids from the subject substance. For example, U.S. Pat. No. 3,939,281 describes a method of extracting and removing fats from starch-containing plants by carbon dioxide extraction, and Japanese Patent Unexamined Publication No. 188053/1985 describes the method of treating the raw material brewing rice by carbon dioxide extraction. However, none of these methods has been reported to be applied to malt for beer brewing. Also, to apply this method to malt for beer brewing, it is necessary to avoid damaging of enzymes in the malt, and the problems with regard to which balance of lipids is appropriate and what the degree of total lipid content is preferable remain to be solved, as stated above.